1. Field of the Invention
The present invention relates to insulating glass paste for forming an over glaze layer, and a thick-film circuit component using the insulating glass paste.
2. Description of the Related Art
In a thick-film circuit component of a hybrid IC or the like, the technique of forming thick-film patterns of thick-film conductors, thick-film resistors, etc. on an insulating substrate is brought into practical use. Particularly, a screen printing method is used for many purposes in order to miniaturize and make the thick-film conductors, thick-film resistors, etc., fine lined
An example of thick-film multilayered circuit components using the thick-film forming technique is described with reference to FIG. 1.
In a thick-film multilayered circuit component 20 comprising an insulating substrate 11 made of alumina or the like, a plurality of first thick-film conductors 12 are printed as wiring on an insulating substrate 11 by screen printing, and an interlayer insulation film 13 mainly composed of glass is formed on the first thick-film conductors 12. Furthermore, a plurality of second thick-film conductors 14 are printed as wiring on the interlayer insulation film 13, and thick-film resistors 15 are partially provided on the second thick-film conductors 14. An over glaze layer (i.e., a protective insulating glass layer) 16 is provided as an uppermost layer for protecting the thick-film conductors 14 and the thick-film resistors 15.
However, cracks 17 occurs in the over glaze layer 16 at the edges of the thick-film conductors 14, the overlap portions with the thick-film resistors 15, etc. in the thick-film multilayered circuit component 20 due to a difference in thermal expansion coefficient between the insulating substrate 11, the thick-film conductors 12, the thick-film resistors 15 or the interlayer insulating film 13 and the over glaze layer 16. The occurrence of the cracks 17 causes deterioration in conductivity of the thick-film conductors 14 or a variation in resistance of the thick-film resistors 15 due to contact of the thick-film conductors 14 and the thick-film resistors 15 with the outside air, causing deterioration in reliability of the thick-film multilayered circuit component 20.
The present invention has been achieved for solving the above problem, and an object of the present invention is to provide insulating glass paste for forming an over glaze layer, which causes less cracks in the formed over glaze.
Another object of the present invention is to provide a thick-film circuit component with high reliability, in which the occurrence of cracks in an over glaze layer is suppressed.
As a result of intensive research of the characteristics of insulating glass paste, such as the thermal expansion coefficient, Young""s modulus, Vickers hardness of the over glaze layer, etc., and the rate of occurrence of cracks, the inventors found that fracture toughness strength (KIC) after burning has a significant relation to the rate of occurrence of cracks.
Namely, the present invention relates to insulating glass paste for forming an over glaze layer, wherein fracture toughness strength after burning is about 1.0 MN/M{fraction (3/2)} or more.
The insulating glass paste of the present invention may include a mixture of an amorphous glass powder, a metal oxide powder and an organic vehicle.
The insulating glass paste of the present invention may include a mixture of an crystallized glass powder and an organic vehicle.
The insulating glass paste of the present invention may include a mixture of a crystallized glass powder, a metal oxide powder, and an organic vehicle.
The present invention also provides a thick-film circuit component comprising an over glaze layer formed for protecting thick-film resistors and/or thick-film conductors provided on a substrate, wherein the over glaze layer is formed by burning the insulating glass paste of the present invention.
The insulating glass paste of the present invention exhibits a fracture toughness strength of about 1.0 MN/m{fraction (3/2)} or more after burning, i.e., it can form the over glaze layer having a fracture toughness strength of about 1.0 MN/m{fraction (3/2)} or more. Therefore, it is possible to form the over glaze layer in which the occurrence of cracks is suppressed by sufficiently absorbing differences between the thermal expansion coefficients of the thick-film conductors, the thick-film resistors, etc.
In the thick-film circuit component of the present invention, since the over glaze layer is formed by burning the insulating glass paste of the present invention, the occurrence of cracks in the over glaze layer is sufficiently suppressed during burning of the over glaze layer and operation of the thick-film circuit component, thereby obtaining the thick-film circuit component having high reliability.